In a gas chromatograph mass spectrometer (GC/MS), components in a sample are temporally separated in a column of a gas chromatograph (GC), and the separated components are sequentially injected into and detected by a mass spectrometer. Since a GC/MS requires a fairly long time to achieve a stable status in which an analyses can be performed from the moment when the power of the apparatus is activated, the power of the apparatus is seldom shut down and the power is generally kept on even if there is a time interval between the end of one analysis and the initiation of the next analysis. However, in actually performing an analysis, it is not uncommon that the time interval between the end of an analysis of one sample and the initiation of an analysis of the next sample is as long as from a few hours to more than a dozen hours. Therefore, there has been a demand for reducing the running cost required for the waiting period until the next analysis as much as possible both from the standpoint of environmental protection and the standpoint of cost reduction in a company or organization.
In the case of a GC/MS, wasteful consumption during the waiting period as previously described is mainly composed of the consumption of a gas (or a carrier gas) which is continuously supplied through the column of the GC and the consumption of the power for warming the column oven and other units and for driving a vacuum pump for evacuating a vacuum chamber. In a GC/MS, if the supply of a carrier gas is completely stopped during the waiting period, the inside of the column, which is connected to a mass spectrometer in a vacuum state, will be evacuated to a substantial vacuum level. This might deteriorate the column, e.g. the liquid phase applied to the inner wall of the column is damaged. Therefore, it is required to keep the carrier gas flowing at a low flow rate also during the waiting period, without stopping the supply of the carrier gas. In addition, a complete halt in heating the column oven during the waiting period causes the problem that it takes time to heat the inner wall of the oven, which has a large heat capacity, and other portion to perform the next analysis. Given these factors, in the GC described in Japanese Unexamined Patent Application Publication No. 2000-304751 for example, a user presets the temperature of a column oven to be approximately as low as the room temperature and presets the flow rate of a gas to be low for the waiting period, and when a daily shutdown (or a waiting mode) is activated, each unit is controlled so that the column oven temperature and the gas flow rate will be at the preset values.
However, conventional GCs have the following problem: with the aim of dealing with a variety of analyses, recent GCs provide a plurality of gas control modes for supplying a carrier gas to a column, such as a constant linear velocity control mode, a constant column flow rate control mode, and a constant pressure control mode. However, in some gas control modes, a decrease in the temperature of a column which extremely decreases the viscosity of the carrier gas may preclude an appropriate control, because, in an actual analysis, it is assumed that the column temperature will not be as low as room temperature for example. In the constant linear velocity control mode for example, the column inlet pressure is controlled so that the linear velocity of the gas flowing in the column is constant. If the viscosity of the carrier gas is extremely decreased, it is required to extremely decrease the column inlet pressure in order to maintain the linear velocity constant, which is beyond the controllable limits.
Particularly in the case of a GC/MS, there is an allowable upper limit of the gas flow rate injectable into a mass spectrometer. If the gas supply control is not appropriately performed as previously described, in some parameter settings, a gas may flow into the mass spectrometer with a flow rate beyond the allowable upper limit, which might cause damage to the mass spectrometer or some other problems.
In addition, in conventional GCs, the temperature of the column oven is maintained at the setting value even in the waiting mode, and the power is basically supplied to the heater which is provided for the column oven. However, in recent years, taking an action for reducing CO2 emission and reducing cost have been further required. To this end, it is indispensable to shut down the power to the heater during the waiting mode. However, if the control is merely stopped to cease the power supply in a column oven having both a heater and an air fan, the temperature in the column oven may in some cases become too high due to the afterheat of the heater and damage the column.